This project will investigate the mechanisms of translational control by mRNA selection on E. coli ribosomes, particularly ribosomes from cells infected with T4 bacteriophage. A reduction of the relative ability of low-salt washed ribosomes to translate f2 RNA but not T4 late RNA occurs in several ways: (1) infection with bacteriophage T4 (T4 ribosomes), (2) treatment of ribosomes from uninfected cells (control ribosomes) with N-ethylmaleimide, and (3) sedimentation of control ribosomes through glycerol gradients. It is believed that because extracts of control ribosomes stimulate translation of f2 RNA on T4 ribosomes they contain ribosomal protein S1. An S1-depleted system will be developed to test the role of S1 in mRNA selection. Particular emphasis will be placed on the sulfhydryl requirements for the stimulatory and inhibitory S1 functions and for S1 to bind to ribosomes. These properties will be analyzed with f2 RNA, T4 early RNA, T4 late RNA, poly U, and STNV RNA. The experimental conditions previously used by others will be systematically analyzed for differences in the translation of RNA phage RNA on T4 ribosomes. T4-Modified S1, or similar ribosomal proteins, will be purified. The T4-modified protein will be compared with host S1 in respect to affinity for ribosomes, sulfhydryl requirements and specificity in translating several mRNA's. Attempts will be made to determine how T4 infection modifies the protein, and if possible, the modification will be reproduced in vitro. Host and T4-S1 will be tested in the DNA-dependent transcription-translation system to see whether T4 early protein synthesis is reduced. Other inhibitory proteins, i.e., gene 32 product, will be tested in the coupled system with vegetative DNA to try to reduce the early protein synthesis and amplify quasi-late and late protein synthesis.